The use of damping devices such as Helmholtz resonators in turbine engines is known to dampen undesired frequencies of dynamics that may develop in the engine during operation. Examples are disclosed in U.S. Pat. No. 6,530,221.
One or more resonators can be attached to a surface of a turbine engine component such as a combustor liner by welding. Some resonators include passages through which air can enter and purge the cavity enclosed by the resonator. One beneficial byproduct of such airflow is that the component to which the resonator is attached can be impingement-cooled. That is, cooling air can pass through the passages and directly impinge on the hot surface underlying the resonator housing. One such example is U.S. Pat. No. 7,089,741 which shows resonators having side walls with cooling holes and an outer wall with purge holes.
The operational demands of some engines have necessitated resonators with greater damping effectiveness, which can be achieved by increasing the size of the resonators. However, a tradeoff to larger resonators is that the cooling holes become less effective in cooling the surface below, especially when resonator height is increased. As the distance between the impingement cooling holes and the hot surface beneath increases, the cooling air can disperse within the cavity of the resonator without impinging on the hot surface. As a result, the cooling is less effective. Thus, there can be concerns of overheating of the component and/or the welds between the resonator and the component, which can reduce the life cycle of these components.
Increased cooling air may be directed through larger resonators to improve cooling, but this reduces the amount of air that becomes premixed with the fuel, thereby providing a richer fuel mixture which burns hotter and can adversely affect emissions. Furthermore, increasing the coolant flow through the resonator can detune the resonator so that it no longer damps in its target frequency range. Alternately, additional resonators can be provided on the component. However, adding resonators at sub-optimal locations can provide less damping effectiveness than a larger resonator at an optimal location. Further, other design constraints, including space limitations, may limit the ability to attach more resonators at other locations.